Seismic attenuation and scattering tomography reveal lithospheric complexity and fluid signatures across the Southern Apennines – Northern Calabrian boundary (South Italy)

Summary The Southern Apennines—Northern Calabrian boundary is a region marked by lithological heterogeneity, complex geodynamics and tectonics, and prone to significant seismic hazard. This sector is part of a complex geodynamic system, where Africa-Eurasia convergence, Ionian subduction, and slab retreat coexist. Its structure and seismic activity derive from extensive lithospheric heterogeneity and fluid-related processes, both of which are poorly constrained. Here, we present a novel application of seismic attenuation and scattering tomography of the area at a regional scale. We estimated seismic wave attenuation and scattering for the Southern Apennines—Northern Calabria region using a dataset of 1581 waveforms related to 95 M ≥ 3.0 earthquakes that occurred between 2004 and 2024 and were recorded at 32 stations. We constrained the heterogeneous properties and fluid saturation of the Southern Apennines—Northern Calabrian region by mapping P-wave Peak Delays and inverting coda-normalized energies for total attenuation (1/Q). Results consistently reveal different seismic energy dissipation mechanisms between the two domains, reflecting their different characteristics in terms of Peak Delay and attenuation patterns. The Southern Apennines exhibit high Peak Delay values at all depths and almost no remarkable total attenuation anomalies, consistent with weakly consolidated, fractured sedimentary sequences and limited fluid content. Nevertheless, at a depth of 5.4 km, a relatively high attenuation pattern is detectable, likely linked to the presence of less cohesive and potentially fluid-saturated units. Conversely, Northern Calabria shows low Peak Delay and high attenuation in the investigated depth range, reflecting wave propagation through coherent crystalline rocks with significant fluid circulation, likely favored by overpressurized materials or active migration pathways. The spatial correlation between high attenuation, low seismic velocities, and thermal anomalies shows that fluids modulate seismic wave behavior, providing new constraints on the crustal structure and seismotectonic segmentation of the region. The joint interpretation of our results with other geophysical models and responses highlights the complex interplay between lithology, tectonics, and fluid dynamics across this critical segment of the central Mediterranean.